More bad news from Yahoo - the company alerted users on Wednesday that potential malicious activity could have affected their accounts between 2015 and 2016.

The announcement came just months after Yahoo confirmed that more than one billion accounts had been compromised through a 2013 security breach. The accessed data included users' names, passwords, security questions and contact information, the company said. Last September, Yahoo revealed that a similar attack targeted 500 million accounts in 2014.

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It's unclear how many users were affected by the breach, which used forged cookies to bypass password-protected accounts.

Yahoo is still investigating the incident. The company said it had "identified user accounts for which we believe forged cookies were taken or used. Yahoo is in the process of notifying all potentially affected account holders."

2. Create strong passwords that use a combination of letters, numbers and symbols. Don’t share it with anyone. Enable any additional security features that verify your identity, especially on financial sites.

3. Don’t click on suspicious links. Be wary of emails or pop-ups that ask for personal information.

4. Keep a close eye on online banking accounts. Only use credit cards that offer protection from fraudulent transactions for online purchases.